Re: Fix crash in vect_is_slp_reduction

[Ira Rosen <IRAR@il.ibm.com>]

gcc-patches-owner@gcc.gnu.org wrote on 20/05/2011 05:17:47 PM:

>
> On Fri, May 20, 2011 at 4:06 PM, Ryan Mansfield <rmansfield@qnx.com>
wrote:
> > There is a crash in vect_is_slp_reduction where use_stmt doesn't get
> > initialized in the FOR_EACH_IMM_USE_FAST loop.
> >
> > 1718          FOR_EACH_IMM_USE_FAST (use_p, imm_iter, lhs)
> > (gdb) call debug_tree(lhs)
> >  <ssa_name 0x7ffff6e3a5a0
> >    type <integer_type 0x7ffff7f8c7e0 int32_t sizes-gimplified public SI
> >        size <integer_cst 0x7ffff7ec47e0 constant 32>
> >        unit size <integer_cst 0x7ffff7ec4580 constant 4>
> >        align 32 symtab 0 alias set -1 canonical type 0x7ffff7ecb498
> > precision 32 min <integer_cst 0x7ffff7ec4780 -2147483648> max
<integer_cst
> > 0x7ffff7ec47a0 2147483647> context <translation_unit_decl
0x7ffff7f98508
> > D.1314>
> >        pointer_to_this <pointer_type 0x7ffff7f9f930>>
> >    var <var_decl 0x7ffff6e1ce60 g_29_lsm.18>def_stmt g_29_lsm.18_137 =
PHI
> > <g_29_lsm.18_87(15), D.2113_96(18)>
> >
> >    version 137>
> > (gdb) n
> > 1742          if (found)
> > (gdb)
> > 1746          if (gimple_code (use_stmt) == GIMPLE_PHI)
> > (gdb)
> >
> > Program received signal SIGSEGV, Segmentation fault.
> > 0x0000000000980f22 in gimple_code (g=0x0) at ../../gcc/gimple.h:1098
> > 1098      return g->gsbase.code;
> >
> > Is the following sufficient?
>
> No, we shouldn't arrive with a NULL use_stmt here.

I think a proper fix will be to fail if there are no uses.
I'll prepare a patch on Sunday.

Ira

Index: tree-vect-loop.c
===================================================================
--- tree-vect-loop.c    (revision 173856)
+++ tree-vect-loop.c    (working copy)
@@ -1704,7 +1704,7 @@ vect_is_slp_reduction (loop_vec_info loop_info, gi
   tree lhs;
   imm_use_iterator imm_iter;
   use_operand_p use_p;
-  int nloop_uses, size = 0;
+  int nloop_uses, size = 0, nuses;
   bool found = false;

   if (loop != vect_loop)
@@ -1715,9 +1715,11 @@ vect_is_slp_reduction (loop_vec_info loop_info, gi
   while (1)
     {
       nloop_uses = 0;
+      nuses = 0;
       FOR_EACH_IMM_USE_FAST (use_p, imm_iter, lhs)
         {
           use_stmt = USE_STMT (use_p);
+          nuses++;
           if (is_gimple_debug (use_stmt))
             continue;

@@ -1739,6 +1741,10 @@ vect_is_slp_reduction (loop_vec_info loop_info, gi
             return false;
         }

+      /* The statement has no uses.  */
+      if (nuses == 0)
+       return false;
+
       if (found)
         break;


>
> Richard.
>
> > Index: tree-vect-loop.c
> > ===================================================================
> > --- tree-vect-loop.c    (revision 173945)
> > +++ tree-vect-loop.c    (working copy)
> > @@ -1743,7 +1743,7 @@
> >         break;
> >
> >       /* This is a loop exit phi, and we haven't reached the reduction
phi.
> >  */
> > -      if (gimple_code (use_stmt) == GIMPLE_PHI)
> > +      if (!use_stmt || gimple_code (use_stmt) == GIMPLE_PHI)
> >         return false;
> >
> >       if (!is_gimple_assign (use_stmt)
> >
> > Regards,
> >
> > Ryan Mansfield
> >